1. Field of the Invention
This invention relates to a pressure cylinder of plastics material, such as a master cylinder or wheel cylinder for use in a vehicle hydraulic braking system for example, and is particularly concerned with the connection of a pressure fluid supply pipe to a port of such a cylinder.
2. Description of the Prior Art
Cylinders of plastics material are not capable of withstanding the stresses imposed by the conventional arrangement employed in metal pressure cylinders in which a pipe nut is engaged in a threaded aperture formed in the cylinder body and tightened to clamp a flared portion of a supply pipe against a seat in the body. Attempts have been made to adapt this conventional arrangement for use with plastic pressure cylinders. In one such adaptation, a separate threaded component is inserted into a guide formation in the plastic cylinder body and receives a pipe nut which clamps a flared pipe end against a seat formed in the body. Although the inserted component sustains the torque arising at the threaded connection between the pipe nut and component, the cylinder body is still required to sustain the high clamp loading at the pipe flare seat. This can be unsatisfactory in practice because of the long term tendency of plastics materials to "creep" away from highly stressed areas, which can give rise to the pipe nut becoming loose with the consequent risk of fluid leakage.
In another adaptation of the conventional pipe nut arrangement, a separate seat member is used in addition to a threaded component, the flared pipe end being clamped against the seat member by a pipe nut screwed into the threaded component, as before. This arrangement exhibits the disadvantage that the separate seat member may be lost in transit or inadvertently omitted during assembly, or when the pipe connection is made, and this can have potentially dangerous consequences in an hydraulic system used for vehicle brake actuation, for example.